1. Field of Invention
The present invention relates to improved electrophotographic copiers and more particularly to such copiers having apparatus for regulating one or more of the copier's operative stations to compensate for changes in the uniformity of copying results which occur during the initial periods of operation after periods of machine rest.
2. Description of Prior Art
U.S. application Ser. No. 621,940, entitled ELECTROPHOTOGRAPHIC APPARATUS HAVING COMPENSATION FOR CHANGES IN SENSITOMETRIC PROPERTIES OF PHOTOCONDUCTORS and filed Oct. 14, 1975, now abandoned, in the name of Curtis L. Stephens discloses improved electrophotographic apparatus having means for compensating for changes in sensitometric properties of reusable photoconductive insulator layers (herein also referred to merely as photoconductors) which occur with increasing cumulative usage of such photoconductors. In general this application discloses that certain photoconductors, particularly organic photoconductors, exhibit a change in sensitometric properties, e.g., a decrease in the ability to discharge electrostatic charge per given exposure, and that those changes can be determined empirically for a particular photoconductor specie and given apparatus configuration and compensated for by an increase in exposure, primary charge and/or development bias according to a predetermined program.
However, I have discovered that another predictable phenomenon operates concurrently with the changes that occur cumulatively over the photoconductor's lifespan. Specifically, we have found that after a period of non-use, or "rest," certain electrophotographic apparatus exhibit a decrease in speed (i.e., rate of electrostatic discharge per given exposure) and then, after a period of usage, or "run" return to a performance predictable according to its cumulative usage by the teachings of the aforementioned application. Whether such temporary "rest-run" shifts in performance of the apparatus results solely from sensitometric changes in the photoconductor, or from such changes in combination with other variables in the overall machine operation during transition between the rest and steady state run condition, is not fully understood. However, I have found that such temporary changes occur in a predetermined manner and can be compensated for in a manner providing increased copy quality.